1. Field of the Invention
The invention relates to the selective fluorination of hydrochlorocarbons and/or hydrochlorofluorocarbons, or mixtures thereof. More particularly, the invention pertains to a process for the preparation of 1,1-dichloro-3,3,3-trifluoropropane (HCFC-243) by the reaction of 1,1,1,3,3-pentachloropropane (HCC-240) with hydrogen fluoride in the presence of an activated hydrofluorination catalyst.
2. Description of the Related Art
It is known in the prior art to produce hydrofluorocarbons (HFC's) by reacting hydrogen fluoride (HF) with various hydrochlorocarbon and hydrochlorofluoro-carbon compounds. HFCs are typically prepared by fluorinating a chlorinated organic compound with a fluorination agent such as hydrogen fluoride in the presence of a fluorination catalyst. In recent years, there has been universal concern that completely halogenated chlorofluorocarbons might be detrimental to the Earth's ozone layer. Consequently, there is a worldwide effort to use fluorine-substituted hydrocarbons which contain fewer or no chlorine substituents. The desired products therefore are organic compounds similar to the organochlorine compound used in which the chlorine atoms have been partially or totally replaced with fluorine atoms. For example, it is known to produce hydrofluorocarbon HFC-245fa (1,1,1,3,3-pentafluoropropane) by the reaction of HCC-240fa (1,1,1,3,3-pentachloropropane) or HCC-1230 (1,3,3,3-tetrachloro-1-propene) with hydrogen fluoride (HF) either in the liquid or vapor phase. See, for example, U.S. Pat. No. 5,710,352 which teaches a method for the preparation of 1,1,1,3,3-pentafluoropropane (HFC-245fa) and 1-chloro-3,3,3-trifluoropropene (HCFC-1233) whereby 1,1,1,3,3-pentachloropropane (HCC-240fa) is fluorinated with HF in a vapor phase in the presence of a vapor phase catalyst.
Such reactions may be conducted in either the liquid or vapor phase. Generally, the liquid phase fluorination is preferred because the reaction is controlled at relatively lower temperatures which results in less by-product formation due to decomposition. Liquid phase fluorination, however, uses and generates corrosive compounds, such as, for example, hydrogen fluoride, hydrogen chloride, and catalysts such as SbCl5 or SbF3Cl2, which form superacids. These superacids tend to corrode the reactor in which the reaction is conducted, even reactors comprised of corrosion-resistant materials such as Inconel 600, NAR25-50MII, Hastelloy C, Hastelloy G-30, duplex stainless steel and Hastelloy C-22. This is primarily due to the concentrations, temperatures and pressures involved and the need for oxidants such as chlorine that are used to maintain catalyst activity. Corrosion of the reactor compromises the structural integrity of the reactor and reduces its useful life. As a result of such extreme corrosive activity of the reaction system on metals, fluoropolymer lined reactors must be used. See, for example, U.S. Pat. No. 5,902,912, which teaches a process for producing hydrofluorocarbons in a fluoropolymer-lined reactor whereby a chlorinated organic compound in liquid phase and a fluorination agent are charged into the reactor and reacted to produce the hydrofluorocarbon. However, these lined reactors suffer from poor heat transfer and HF permeation of the liner, and the use of chlorine as an oxidant results in yield loss due to the chlorination of various materials, intermediates, and reactants.
It has been determined that these known processes are not economical relative to their product yield. It is consequently advantageous to have available an efficient hydrofluorination process allowing chlorine atoms to be replaced with fluorine atoms more easily and with high selectivity. The present invention provides an improved process for the preparation of hydrofluorocarbons with a high yield. The processes of the invention involve the reaction of a hydrocarbon with hydrogen fluoride in the presence of an activated fluorination catalyst. Particularly effective fluorination catalysts for obtaining a high yield include chlorides of metals from groups IV, V, XIV, and XV of the Periodic Table of the Elements that have been first activated by their reaction with hydrogen fluoride. More particularly, the invention provides a process for the preparation of 1,1-dichloro-3,3,3-trifluoropropane (HCFC-243) from 1,1,1,3,3-pentachloropropane (HCC-240) with a very high yield. HCFC-243 is an important precursor to the agricultural intermediate HCFC-233, i.e. trichlorotrifluoropropane.